1. Field of the Invention
This invention relates to a liquid jet recording head, and more particularly to a recording head for generation of small droplets of a liquid for recording to be used in a liquid jet recording system in which recording is performed by generating small droplets of a liquid for recording such as ink, etc., and attaching them onto a recording medium such as paper.
2. Related Background Art
The liquid jet recording system which performs recording by generating small droplets of a liquid for recording such as ink, etc., and attaching them onto a recording medium such as paper is attracting attention as the recording system which generates very little noise during recording, and also is capable of high speed recording and further enables recording on a plain paper without requiring any special treatment such as fixing. Various types of this system having been actively studied.
The recording head portion of the recording device to be used in the liquid jet recording system generally consists of an orifice for discharging a liquid for recording (liquid discharging outlet), a liquid passage connected to the orifice and having a portion at which the energy for discharging the liquid for recording acts on the liquid for recording and a liquid chamber for storing the liquid for recording to be fed into the liquid passage.
The energy for discharging the liquid for recording during recording is generated in most cases by means of a discharge energy generating element of various types such as a heat generating element, piezoelectric element, etc., which is arranged at a predetermined position at the portion where the discharging energy is permitted to act on the liquid for recording which constitutes a part of the liquid passage (energy acting portion).
As methods for preparing the liquid jet recording head with such a constitution, there have been known, for example, the method comprising the steps of forming fine grooves on a flat plate of glass, metal, etc., by cutting or etching and bonding another appropriate plate onto the flat plate having such grooves formed thereon to thereby form liquid passages or the method comprising the steps of forming groove walls of a cured photosensitive resin on a substrate having a discharging energy generating element arranged thereon according to a photolithographic step to provide grooves for the liquid passages on the substrate and bonding another flat plate (covering) onto the grooved plate thus formed to thereby form liquid passages (for example, Japanese Laid-open Patent Application No. 43876/1982).
Of these methods for preparation of the liquid jet recording heads, the latter method employing a photosensitive resin is more advantageous than the former method in that liquid jet recording heads can be provided with better quality and cheaper cost because it enables fine working with better precision and better yield and easier production.
As the photosensitive resin to be used in preparation of such recording heads, there have been employed those used for pattern formation in printing plates or printed-wiring or those known as the photocurable coating materials or adhesives to be used for glass, metal, ceramics, etc. Also, in aspect of working efficiency, dry film type resins have been primarily utilized.
In the recording head employing a cured film of a photosensitive resin, in order to obtain excellent characteristics such as high recording characteristic, durability and reliability, etc., the photosensitive resin to be used for the recording head is required to have the following characteristics:
(1) particularly, excellent adhesion of the cured film to a substrate; PA1 (2) excellent mechanical strength and durability, etc., when cured; and PA1 (3) excellent sensitivity and resolution during patterning by use of pattern exposure light. PA1 (i) a linear polymer having a glass transition temperature of 50.degree. C. or higher and a weight-average molecular weight of about 3.0.times.10.sup.4 or more; and (ii) an epoxy resin comprising at least one compound having two or more epoxy groups in the molecule, the epoxy groups existing in said epoxy resin being partially esterified with an unsaturated carboxylic acid.
However, under the present situation, none of the photosensitive resins used for formation of the liquid jet recording head hitherto known in the art satisfy all of the above requisite characteristics.
To describe in more detail, those employed for pattern formation in printing plates, printed-wirings, etc., as the photosensitive resin for recording head are inferior in adhesion or close contact with glass, ceramics, plastic film, etc., to be used as the substrate, although they are excellent in sensitivity and resolution, and also insufficient in mechanical strength and durability when cured. For this reason, as the stage of preparation of recording heads, or in the course during usage, there is involved the drawback that deformation of the resin cured film or peel-off from the substrate or damages are liable to occur, which may cause marked impairment of reliability of the recording head such as lowering in recording characteristics by impeding the flow of the liquid for recording in the liquid passages or making the liquid droplet discharging direction unstable.
On the other hand, those which are known as photocurable type coating materials or adhesives to be used for glass, metals, ceramics, etc., although having advantages of excellent close contact or adhesiveness with the substrate formed of these materials and also satisfactory mechanical strength and durability obtained when cured, are inferior in sensitivity and resolution and therefore require an exposure device of higher intensity or an exposure operation for a longer time. Further, their inherent characteristics cannot afford a precise and high density pattern with good resolution, whereby there is involved the problem that it is not suitable for a recording head for which minute precise working is particularly required.